Added support for nested multigeometries with test coverage

[ericmassip]

Closes #52

Nested multigeometries is a valid use case, as the docs say. This PR adds support for nested multigeometries. They work the same way as first level multigeometries, to extract the geoms from one just call .geoms again.

E.g.:

first_multigeometry_geoms = first_multigeometry.geoms

# If first_multigeometry only has one geometry and it is a nested multigeometry
second_multigeometry_geoms = list(first_multigeometry.geoms)[0].geoms

[what-the-diff]

PR Summary

• New Test Case Added
  A new test case has been added to cover nested MultiGeometry scenarios.
• Bug Fix in _get_multigeometry() Function
  The bug that affected handling of nested MultiGeometries has been fixed.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.02 🎉

Comparison is base (6bb9374) 93.00% compared to head (cf87477) 93.02%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #226      +/-   ##
===========================================
+ Coverage    93.00%   93.02%   +0.02%     
===========================================
  Files           26       26              
  Lines         4418     4432      +14     
===========================================
+ Hits          4109     4123      +14     
  Misses         309      309              

Impacted Files	Coverage Δ
fastkml/geometry.py	94.75% <100.00%> (+0.10%)	⬆️
tests/oldunit_test.py	99.83% <100.00%> (+<0.01%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.